An Active Matrix Organic Light Emitting Diode (AMOLED) display has been widely applied due to its wide angle of view, good color contrast effect, high response speed, self-illuminating and other advantages.
An AMOLED typically adopts low-temperature polysilicon as a drive layer to implement its pixel drive circuit. As compared with a general amorphous-silicon process, the low-temperature polysilicon thin film transistor characterized by its higher mobility and more stability is more suitable for the AMOLED display.
At present, a pixel circuit illustrated in FIG. 1 is typically adopted in a large-size display panel, where drive currents of all the pixels is provided by the same power source VDD. A power line on a backboard for directing the power source VDD to pixels in respective rows has a certain resistance, and the respective rows of pixels are lighted constantly, so current flows over the power line all the time, and consequently the voltage on the power line varies at the different rows of pixels. For example, if the voltage on the power line is VDD−1 at the first row of pixels and VDD−n at the n-th row of pixels, then VDD−1 is larger than VDD−n by an amount dependent on the current on the power line and the resistance of the power line. Moreover, a picture displayed by the display panel is changing constantly, so the current flowing through the power line is also changing constantly, so that the voltage at the n-th row of pixels may be indeterminate, that is, with the same data signal received at the n-th row of pixels at different moments, the current flowing through the power line is changing, so that the voltage difference between the gate of a drive transistor M3 and the source of the drive transistor M3 is also changing and consequently the current driving a diode OLED to emit light is changing, thus resulting in a poor display effect.
In FIG. 1, the pixel circuit further includes a P-type transistor M1, a P-type transistor M2, a P-type transistor M3, a P-type transistor M4, a P-type transistor M5, a P-type transistor M6, a capacitor C1, a capacitor C2, and an OLED, where the gate of the P-type transistor M1 and the gate of the P-type transistor M6 receive an emitted signal EMIT, the gate of the P-type transistor M5 receives a first scan signal SCANT, the gate of the P-type transistor M2 and the gate of the P-type transistor M3 receive a second scan signal SCAN2, and the source of the P-type transistor M5 receives a reference signal Vref.